Field of the Invention
The present invention relates to a cooling technique for a light source used in lithography or the like.
Description of the Related Art
An exposure apparatus is an apparatus that transfers the pattern of an original (reticle or mask) onto a photosensitive substrate (for example, a wafer or glass plate with a resist layer formed on the surface) via a projection optical system in a lithography process that is a manufacturing process of a semiconductor device, a liquid-crystal display device, or the like. For example, a projection exposure apparatus that transfers a pattern onto a liquid-crystal display device is recently required to expose a larger area pattern on a mask onto a substrate at once. To meet this requirement, a step-and-scan type scanning projection exposure apparatus capable of attaining a high resolving power and exposing a larger screen has been proposed. The scanning exposure apparatus exposes and transfers a pattern illuminated with a slit light beam onto a substrate by a scanning operation via a projection optical system.
In such a scanning exposure apparatus, a high output light source such as a discharge lamp is used to improve productivity. An illumination optical system with the light source includes not only an electrode wire but also a cooling unit aiming at cooling a bayonet cap portion (heat generating portion). The electrode wire and the cooling unit are arranged close to the light source unit for conduction and heat transfer, and therefore cast a shadow on exposure light and adversely affect the effective light source. An effective light source distribution is a light intensity distribution on the pupil plane of an illumination optical system that illuminates a mask. Hence, to minimize the adverse effect on the effective light source distribution, the electrode wire and the cooling unit need to be made small. Japanese Patent Laid-Open No. 2008-262911 discloses an arrangement in which a refrigerant flow channel is provided in the bayonet cap portion (heat generating portion) of a discharge lamp, thereby integrating a cooling unit and the light source unit.
In the technique of Japanese Patent Laid-Open No. 2008-262911, however, it is believed that the mechanism for providing the refrigerant flow channel in the electrode portion of the discharge lamp makes the electrode portion large and therefore cannot simply lead to minimization of the influence on the effective light source distribution. Additionally, the electrode portion of the discharge lamp becomes complex, resulting in a high cost of the discharge lamp.